Heretofore, cubic spinel-type ferrites as represented by Mn—Zn ferrite have been used in high frequency devices by taking advantage of their high magnetic permeability. However, upon use in frequencies of several hundred MHz, the permeability of the cubic spinel-type ferrites is sharply deteriorated due to their Snoek's limit, and the effectiveness as material for high-frequency devices will disappear. Among hexagonal ferrites, a ferroxplana-type ferrite with the c-plane having a high magnetizability is expected as noteworthy material for high frequency devices to be used in higher frequency range, because it can maintain a high magnetic permeability up to several GHz beyond the Snoek's limit of cubic spinel-type ferrites. The ferroxplana-type ferrite has a typical composition of Ba2Zn2Fe12O22 or Ba3Co2Fe24O41. There have also been known more complicated compositions such as a composition including SiO2 and CaO in addition to the above composition (Japanese Patent Laid-Open Publication No. H09-129433) or Ba3Co2 (Mx, Nx) Fe24-2xO41 (M: divalent metal ion such as Zn, Cu or Co; N: quadrivalent metal ion such as Ti, Zr, Hf, Si, Ge, Sn or Ir; x: 3 or less; Japanese Patent Laid-Open Publication No. 2000-235916). These hexagonal ferrites have been used as powder material for a sintered body (Japanese Patent Laid-Open Publication No. H09-129433) or powder paste for a coated layer (Japanese Patent Laid-Open Publication No. H09-205031).
Recently, in connection with advance of information and communications apparatuses such as portable phones and personal computers, downsizing and increase in signal frequency of electronic devices have been accelerated, which leads to the need for developing high-frequency electronic devices such as a filter or inductor available in higher frequency range with more downsized structure. As a recent trend in downsizing, in view of the limit of a traditional approach of 3-dimensionally downsizing a bulk device, a planer device effective to downsizing and integration is actively developed by utilizing a technology of laminating thin films. However, despite of the strong need in small devices, no technology of forming a thin film using a ferroxplana-type ferrite has been successfully developed.
As shown in FIG. 1, a hexagonal ferrite has M-type, U-type, W-type, X-type, Y-type and Z-type phases, and these phases have different solid-solution ranges, respectively. In addition, the crystal structure in each of the phases is extremely complicated as illustrated in FIG. 2. Thus, while there have been reported many cases of the formation of M-type (BaFe12O19) thin films which is binary system and has perpendicular magnetic anisotropy, none of the formation of other type hexagonal ferrite thin films has been reported. The M-type hexagonal ferrite is a magnetoplumbite-type ferrite having uniaxial anisotropy, and is thereby used for quite different purposes from those of other type hexagonal ferrites. Therefore, the need for developing a technology of forming a Y-type hexagonal ferrite thin film usable in high frequency devices strongly exists.